A typical configuration for a complex electronic system, such as a computer, is a rack mount in which a plurality of circuit cards are mounted in slots within a cabinet. The cards have pin connectors that engage a back plane which is wired to provide the inner connection between the cards. A power supply is conventionally included within the cabinet to provide electrical power for operating the circuit cards. There are typically many connections between the circuit cards and the back plane wherein the connections provide data channels, control signals and power.
In the testing or maintenance of such a system it is frequently necessary to remove one of the circuit cards. If this is done while the system is under power, there is an abrupt and uneven break in the data and power lines. This break can produce noise signals which are transmitted through the communications and control lines and can possibly cause the loss of data or produce an undesired control response. It has, therefore, become the conventional practice to disconnect power for a whole system before any of the circuit cards in it are removed. However, in many cases it is desirable to remove one circuit card while the reminder of the system continues to function. This can be to aid in the diagnosis of a problem or to permit the continued processing of data by the reminder of the system.
In view of these problems there exists a need for apparatus and circuitry to permit a circuit board to be removed from a system, while the system is powered, without the production of undesired transient or control signals that could interrupt the operation of the system.